In recent years, OTT-V (Over The Top Video) has become mainstream in the streaming services on the Internet. One technique that has started to come into wide use as the fundamental technology for OTT-V is MPEG-DASH (Moving Picture Experts Group phase-Dynamic Adaptive Streaming over HTTP (HyperText Transfer Protocol)) (see, for example, NPL 1).
According to MPEG-DASH, a distribution server provides encoded streams having different bit rates for one moving-image content, and a playback terminal demands encoded streams having an optimum bit rate, thereby realizing adaptive streaming distribution.
MPEG-DASH (Spatial Relationship Description) extension defines SRD indicating the position on a screen of one or more individually encoded regions into which an image of a moving-image content has been divided (see, for example, NPLs 2 and 3). The SRD makes it possible to realize a ROI (Region of Interest) function of spatial adaptation for selectively acquiring an encoded stream of an image of a desired regions, using a bitrate adaptation method for selectively acquiring encoded streams having desired bit rates.
Images of moving-image contents include not only images captured through angles of field by a single camera, but also entire celestial sphere images where images captured horizontally around 360° or vertically around 180° are mapped onto 2D (Two-Dimensional) images (planar images), and panoramic images captured horizontally around 360°. For example, if an entire celestial sphere image is to be divided horizontally into three or more regions and the regions are to be encoded, then since the regions at both horizontal ends represent contiguous images, they can be encoded as one image.
However, inasmuch as the positions on the screen of the regions at both ends are discrete, there are a plurality of positions on the screen of objects to be encoded. According to MPEG-DASH, therefore, the positions on the screen of the regions at both ends cannot be described using an SRD. In other words, an SRD is unable to describe the position on a screen of an image made up of a plurality of divided images compatible with encoded streams.
According to an SRD, the positions on a screen of respective regions and positions on images compatible with encoded streams are described as identical to each other. Therefore, if the positions on a screen of respective regions and positions on images compatible with encoded streams are different from each other, the positions on the screen of the respective regions cannot be described using the SRD. In other words, if the positions on the screen of respective divided images that make up an image and positions on images compatible with encoded streams are different from each other, then an SRD is unable to describe the positions on the screen of the respective divided images.